Method of manufacturing ABS resin molded part and ABS resin molded part

ABSTRACT

An ABS resin molded part is manufactured by forming a molded part of an ABS resin into which a particulate filler is mixed, eluting butadiene particles from the surface of the molded part by etching, and forming a plating coat on the surface after the etching.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2005-017324, filed on Jan. 25, 2005, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a plated ABSresin molded part and to an ABS resin molded part.

2. Description of the Related Art

Heretofore, an injection molded part of an ABS resin has been widelyused in electronic and electric equipment, and various kinds of platedpart manufacturing methods have been proposed (See Japanese UnexaminedPatent Application Publication No. Hei 5-59587 and Japanese UnexaminedPatent Application Publication No. Hei 5-230276). In particular, withgreater demands for miniaturization, cost reduction, and so on to theelectronic equipment in recent years, there have been great demands fora reduction in the thickness of plating because an increase in the timetaken for the plating process, which is in proportion to the thicknessof plating, causes higher cost.

However, when thin film is plated on an injection molded part of an ABSresin having a thick walled part and a thin walled part adjoining witheach other, there is a problem of uneven plating, especially in the thinwalled part. Accordingly, in order to improve the yield of the part insuch a case, the thickness of plating has to be large to a certainextent in actual conditions.

Note that Japanese Unexamined Patent Application Publication No. Hei5-59587 and Japanese Unexamined Patent Application Publication No. Hei5-230276 disclose techniques of improving plating adhesiveness and soon, however, they do not describe reducing uneven plating on thematerial surface of the ABS resin molded part having the thick walledpart and the thin walled part adjoining with each other.

SUMMARY OF THE INVENTION

The present invention has been made in view of solving theabove-described problems of the related art. The object thereof is toprovide a means for greatly reducing uneven plating when applying thinfilm plating to an injection molded part of an ABS resin.

According to a first aspect of the present invention, a method ofmanufacturing an ABS resin molded part includes the steps of: forming amolded part of an ABS resin into which a particulate filler is mixed;eluting butadiene particles from a surface of the molded part byetching; and forming a plating coat on the surface after the etching.

In the above-described first aspect, it is preferable that the moldedpart be formed by injection molding the ABS resin into a mold andinclude a thick walled part and a thin walled part adjoining with eachother. Preferably, a thickness of the plating coat be 10 μm or less, andthe filler be carbon black. Preferably, an average particle diameter ofthe filler be 0.5 μm or less. Preferably, the ABS resin contains thefiller at 0.1 wt % or more to 0.5 wt % or less.

According to a second aspect of the present invention, an ABS resinmolded part is such that an ABS resin into which a particulate filler ismixed is injection molded, and butadiene particles is eluted from asurface of the injection molded ABS resin by etching, and a plating coatis formed on the surface after the etching.

Further, according to a third aspect of the present invention, an ABSresin molded part includes: an injection molded part made of an ABSresin into which a particulate filler is mixed; etching pits formed on asurface of the injection molded part by etching butadiene particles; anda plating coat formed on the surface of the injection molded part.

Here, it is preferable that the injection molded part in theabove-described second aspect or third aspect include a thick walledpart and a thin walled part adjoining with each other. In theabove-described second aspect and third aspect, preferably, a thicknessof the plating coat be 10 μm or less. Preferably, the filler be carbonblack. Preferably, an average particle diameter of the filler be 0.5 μmor less. Preferably, the ABS resin contain the filler at 0.1 wt % ormore to 0.5 wt % or less.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, principle, and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by identical reference numbers, in which:

FIG. 1A to FIG. 1C shows butadiene particles and shapes of etching pitsin an ABS injection molded part of the present embodiment; and

FIG. 2A to FIG. 2C shows butadiene particles and shapes of etching pitsin a conventional ABS injection molded part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A manufacturing method of an ABS resin molded part having a plating coataccording to an embodiment of the present invention will be describedbelow.

Firstly, carbon black is mixed as a particulate filler into an ABS resinand dispersed. Then, the ABS resin into which the carbon black is mixedis injected into a mold by an injection molding machine to form an ABSresin molded part including a step portion where a thick walled part anda thin walled part adjoin with each other.

Secondly, the ABS resin molded part made in the above-described firstprocess is degreased, and thereafter etched. By the etching, butadieneparticles are decomposed by oxidation and eluted from the surface of theABS resin molded part. Thereby, innumerable minute holes (etching pits)are formed on the surface of the material. It is known that theadhesiveness between the material surface and the plating coat isimproved through the above-described etching processing since platingmetal is embedded into the etching pits in the plating process (anchoreffect). In this embodiment, as described later, nearly circular andalmost isotropic etching pits are formed substantially evenly on thesurface of the ABS resin molded part. The etching pits are less orientedin a direction in which the resin flows. Accordingly, the density ofetching pits does not differ much in-between the thin walled part andthe thick walled part of the molded part.

Thirdly, the etched ABS resin molded part is catalytically treatedthrough a catalyser-accelerator process or the like. Thereafter, thecatalytically treated surface is chemically plated and thenelectroplated. Thus, the plating coat is formed on the ABS resin moldedpart.

In this embodiment, the carbon black is mixed into the ABS resin inorder to reduce uneven plating which occurs in the thin walled part ofthe ABS above-described resin molded part when plated. The inventors ofthe present invention presumes the cause of the uneven plating in thethin walled part based on later-described experimental results andacquires the following findings.

The ABS resin at the time of injection molding flows in the mold with anAS phase 11 of acrylic and styrene turned into a liquid state butbutadiene remaining in a particulate state. The butadiene particles 12in the ABS resin have the property of expanding and contracting byexternal force. Therefore, the shapes of the butadiene particles 12 inan ABS resin molded part 10 change according to molding conditions, theshape of the mold, and so on. More specifically, when the molded part 10includes the step portion where the thick walled part and the thinwalled part adjoin with each other, the shapes of the butadieneparticles 12 in the thick walled part and the thin walled part differ asfollows.

The narrower the width of the mold (thin walled part of the molded part)is, the faster the ABS resin flows and the larger the resistance actingon the butadiene particles 12 is. Namely, in the narrow portion of themold, the ABS resin flows at high speed, and the butadiene particles 12are extended by the resistance in a direction where the resin flows.Accordingly, in the thin walled part of the molded part 10, thebutadiene particles 12 tend to be transformed into a flat shape. On theother hand, the ABS resin flows at relatively low speed in a wideportion of the mold, so that, roughly spherical shape of the butadieneparticles 12 is maintained in the thick walled part of the molded part10 without being transformed so much (See FIG. 2A).

Accordingly, flat, shallow, and large etching pits 14 are formed on thesurface of the thin walled part in the etched step portion while nearlycircular, almost isotropic, and small etching pits 14 are formed on thesurface of the thick walled part (See FIG. 2B and FIG. 2C). This causesa difference in the density of etching pits between the thin walled partand the thick walled part of the molded part. Therefore, it isconceivable that uneven plating is very apt to occur in thin filmplating of a film thickness of 10 μm or less because it is particularlysusceptible to the influence on the material surface. Note that in thecase of the thin film plating of the film thickness of 10 μm or less, itis desirable that the thickness of a plating coat be usually 6 μm ormore, but a thickness less than 6 μm is also possible.

FIG. 1A to FIG. 1C shows a state where carbon black 13 is mixed into theABS resin. In FIG. 1A to FIG. 1C, the carbon black 13 enters between thebutadiene particles 12 of the ABS resin. At the injection molding, thebutadiene particles 12 flow, holding the carbon black 13, so that thebutadiene particles 12 are not greatly transformed even in the narrowportion of the mold (See FIG. 1A). Hence, in this case, the shapes ofthe butadiene particles 12 which solidify at the material surfaces ofthe thin walled part and the thick walled part become almost uniform,reducing the difference in the density of the etched etching pits 14consequently (See FIG. 1B and FIG. 1C). As described above, it isconceivable that in this embodiment, unevenness in thin film plating isnot apt to occur.

If the average particle diameter of the carbon black exceeds 0.5 μm, theadhesiveness between the material surface and the plating coat and theappearance of the plating coat deteriorate. Therefore, it is desirablethat the average particle diameter of the carbon black mixed into theABS resin be 0.5 μm or less. Moreover, it is desirable that the averageparticle diameter of the carbon black be 0.2 μm or more, but a particlediameter less than 0.2 μm is also possible.

Further, it is desirable that the ABS resin contain the carbon black at0.1 wt % or more to 0.5 wt %, or less because of the following reasons.If the carbon black content is less than 0.1 wt %, the butadieneparticles are transformed in the thin walled part due to a little carbonblack, and uneven plating is conspicuous in thin plating coat. On theother hand, if the carbon black content exceeds 0.5 wt %, it results inoveretching, worsening the state of the surface after plating.

EXAMPLES

Examples of the present invention will be described below. Through theexperiment, five kinds of specimens with the same shape are formed bythe injection molding machine, using four kinds of ABS resins differentin the average particle diameter of the carbon black and carbon blackcontent, and an ABS resin containing no carbon black. Here, UMG CYCOLAC3001M is used as the ABS resin. The shape of each of the specimens isset to include the step portion where the thick walled part and the thinwalled part adjoin with each other.

Then, each of the specimens is subjected to degreasing, etching,catalytic treatment, chemical plating, and electroplating in order, anda plating coat with a thickness of 10 μm is formed on the surfacethereof. Thereafter, the state of the surface of the plating coat oneach specimen is evaluated visually. Results thereof will be shown inTable 1. TABLE 1 AVERAGE PATRTICLE CARBON STATE OF DIAMETER OF BLACKSURFACE CARBON BLACK CONTENT PLATING (μm) (wt %) COAT COMPARATIVE — — XEXAMPLE EXPERIMIMENT 1 0.2 0.1˜0.2 ◯ EXPERIMIMENT 2 0.5 0.1˜0.2 ◯EXPERIMIMENT 3 0.2 0.3˜0.5 ⊚ EXPERIMIMENT 4 0.5 0.3˜0.5 ⊚⊚: EVEN◯: VERY SLIGHTLY UNEVENX: DISTINCTLY UNEVEN

In Experiment 1 (average particle diameter: 0.2 μm, content: 0.1 wt % to0.2 wt %) and Experiment 2 (average particle diameter: 0.5 μm, content:0.1 wt % to 0.2 wt %), a substantially good plated surface is obtainedon each of the specimens although very slightly uneven plating is foundin the thin walled parts thereof. Further, in Experiment 3 (averageparticle diameter: 0.2 μm, content: 0.3 wt % to 0.5 wt %) and Experiment4 (average particle diameter: 0.5 μm, content: 0.3 wt % to 0.5 wt %), avery good plated surface is obtained on the specimens without unevennessin plating between the thin walled part and the thick walled part.However, remarkable uneven plating is found on the surface of thespecimen without carbon black (comparative example).

(Supplementary Description of Embodiment)

The above-described embodiment describes the example in which the carbonblack is mixed as the particulate filler into the ABS resin. However,any other particulate filler can be used as long as it can maintain itssolid state at a temperature when the ABS resin is injection molded andsuppress transformation of the butadiene particles at the time of theinjection molding.

For example, particles of an organic filler of glass beads, silica,quartz powder, glass powder, silicate (calcium silicate, kaoline, talc,clay, diatomaceous earth, or the like), metal oxide (iron oxide,titanium oxide, zinc oxide, alumina, or the like), metal carbonate(calcium carbonate, magnesium carbonate, or the like), sulfate (calciumsulfate, barium sulfate, or the like), ceramics (silicon carbide, boronnitride, or the like) may be mixed into the ABS resin.

Further, the above-described embodiment describes the example in whichthe thin film plating is formed on the ABS resin molded part includingthe step portion where the thick walled part and the thin walled partadjoin with each other. However, the present invention is alsoapplicable to a case where the thin film plating is formed on an ABSresin molded part including a portion whose thickness increases ordecreases continuously.

The invention is not limited to the above embodiments and variousmodifications may be made without departing from the spirit and scope ofthe invention. Any improvement may be made in part or all of thecomponents.

1. A method of manufacturing an ABS resin molded part, comprising thesteps of: forming a molded part of an ABS resin into which a particulatefiller is mixed; eluting butadiene particles from a surface of themolded part by etching; and forming a plating coat on the surface afterthe etching.
 2. The method according to claim 1, wherein said moldedpart is formed by injection molding the ABS resin into a mold andincludes a thick walled part and a thin walled part adjoining with eachother.
 3. The method according to claim 1, wherein a thickness of saidplating coat is 10 μm or less.
 4. The method according to claim 1,wherein said filler is carbon black.
 5. The method according to claim 1,wherein an average particle diameter of said filler is 0.5 μm or less.6. The method according to claim 1, wherein said ABS resin contains saidfiller at 0.1 wt % or more to 0.5 wt % or less.
 7. The method accordingto claim 2, wherein a thickness of said plating coat is 10 μm or less.8. The method according to claim 7, wherein said filler is carbon black.9. The method according to claim 7, wherein an average particle diameterof said filler is 0.5 μm or less.
 10. The method according to claim 7,wherein said ABS resin contains said filler at 0.1 wt % or more to 0.5wt % or less.
 11. The method according to claim 8, wherein an averageparticle diameter of said filler is 0.5 μm or less.
 12. The methodaccording to claim 11, wherein said ABS resin contains said filler at0.1 wt % or more to 0.5 wt % or less.
 13. The method according to claim8, wherein said ABS resin contains said filler at 0.1 wt % or more to0.5 wt % or less.
 14. An ABS resin molded part, wherein: an ABS resininto which a particulate filler is mixed is injection molded; butadieneparticles is eluted from a surface of the injection molded ABS resin byetching; and a plating coat is formed on the surface after the etching.15. The ABS resin molded part according to claim 14, wherein: said ABSresin molded part includes a thick walled part and a thin walled partadjoining with each other; and a thickness of said plating coat is 10 μmor less.
 16. The ABS resin molded part according to claim 14, whereinsaid filler is carbon black with an average particle diameter of 0.5 μmor less.
 17. An ABS resin molded part, comprising: an injection moldedpart made of an ABS resin into which a particulate filler is mixed;etching pits formed on a surface of said injection molded part byetching butadiene particles; and a plating coat formed on the surface ofsaid injection molded part.
 18. The ABS resin molded part according toclaim 17, wherein said injection molded part includes a thick walledpart and a thin walled part adjoining with each other.
 19. The ABS resinmolded part according to claim 17, wherein a thickness of said platingcoat is 10 μm or less.
 20. The ABS resin molded part according to claim17, wherein said filler is carbon black.
 21. The ABS resin molded partaccording to claim 17, wherein an average particle diameter of saidfiller is 0.5 μm or less.
 22. The ABS resin molded part according toclaim 17, wherein said ABS resin contains said filler at 0.1 wt % ormore to 0.5 wt % or less.
 23. The ABS resin molded part according toclaim 18, wherein a thickness of said plating coat is 10 μm or less. 24.The ABS resin molded part according to claim 23, wherein said filler iscarbon black with an average particle diameter of 0.5 μm or less.